Initial data commit

Task/Floyd-Warshall-algorithm/EchoLisp/floyd-warshall-algorithm.l

@@ -0,0 +1,41 @@
+(lib 'matrix)
+
+;; in : initialized dist and next matrices
+;; out : dist and next matrices
+;; O(n^3)
+
+(define (floyd-with-path n dist next (d 0))
+    (for* ((k n) (i n) (j n))
+     #:break (< (array-ref dist j j) 0) => 'negative-cycle
+    (set! d (+ (array-ref dist i k) (array-ref dist k j)))
+     (when (< d (array-ref dist i j))
+         (array-set! dist i j d)
+         (array-set! next i j (array-ref next i k)))))
+
+;; utilities
+
+;; init random edges costs, matrix 66% filled
+(define (init-edges n dist next)
+   (for* ((i n) (j n))
+    (array-set! dist i i 0)
+    (array-set! next i j null)
+    #:continue (= j i)
+    (array-set! dist i j Infinity)
+     #:continue (< (random) 0.3)
+     (array-set! dist i j (1+ (random 100)))
+    (array-set! next i j j)))
+
+;; show path from u to v
+(define (path u v)
+    (cond
+     ((= u v) (list u))
+     ((null? (array-ref next u v)) null)
+     (else (cons u (path (array-ref next u v) v)))))
+
+(define( mdist u v) ;; show computed distance
+      (array-ref dist u v))
+
+(define (task)
+     (init-edges n dist next)
+     (array-print dist) ;; show init distances
+     (floyd-with-path n dist next))